The invention relates to new liquid crystalline compounds, mixtures of those compounds and their application in optical and electro-optical devices. More particularly, it relates to the use of a component of a polymerisable liquid crystalline mixture in the production of orientated liquid crystalline polymers; compounds used as components in polymerisable liquid crystalline mixtures; liquid crystalline mixtures comprising these components; liquid crystalline polymers prepared from such components; and liquid crystalline devices comprising those compounds.
Liquid crystal polymers (LCPs) are used in the manufacture of optical components such as waveguides, optical gratings, filters, retarders, piezoelectric cells and non-linear optical cells and films. The choice of LCP for use in any one of these optical components depends upon its associated optical properties such as the optical anisotropy, refractive index, transparency and dispersion.
LCPs are manufactured by orientating a layer of a polymerisable liquid crystal single compound or mixture on an orientated substrate and cross-linking that layer to form a liquid crystal polymer (LCP) network. The configuration imposed by the orientation layer on the polymerisable LC single compound or mixture becomes fixed or frozen into the LCP network formed on cross-linking. The resulting LCP films are characterised by a high viscosity and are stable to mechanical stresses, temperature and light exposure. It is highly desirable that the polymerisable LC compounds used in the manufacture of the LCPs are chemically and thermally stable, stable to electromagnetic radiation, soluble in standard solvents and miscible with other LC components. The compounds should also exhibit liquid crystalline properties over the range 0 to 150xc2x0 C., preferably 25 to 100xc2x0 C.
Polymerisable liquid crystal compounds are known from EP 0 748 852, EP 0 700 981, EP 0 699 731, US 5 567 349, WO 97/00600, WO 98/52905 and WO 95/22586. These compounds are characterised by a relatively narrow liquid crystal range.
Materials comprising LCPs are generally prepared from a mixture of components, which includes at least one polymerisable LC single compound. The properties of the LCP material thus prepared depend upon the nature and properties of the components comprising the mixture. It is highly desirable that the components used in the preparation of the LCP materials are compatible. If the components of the mixture are incompatible, the corresponding mixtures may possess thermodynamic properties that make them unsuitable for use in LC devices. Incompatible LC mixtures are characterised by properties such as a depression of the clearing point, a reduction in the liquid crystalline range and problems in achieving a uniform orientation of the LCP material in the preparation of devices.
There is therefore a need for a liquid crystalline single compound or mixture which exhibits a broad liquid-cnrstalline thermal range and which can, alternatively or additionally, be orientated on a substrate prior to cross-linking in such a way that the orientation of the LC single compound or mixture on the substrate remains stable over the period required for manufacturing the LCP network. There is also need for further liquid crystalline mixture components that are compatible with the other components of a liquid crystal mixture.
It has been surprisingly found that by using certain long chain compounds containing at least one mesogenic group, it is possible to prepare mixtures and materials having the ability to address, at least in part, the needs described above.
A first aspect of the invention provides a compound of formula I: 
wherein
A1 to A4 are independently selected from the group consisting hydrogen, a methyl group and a hydrocarbon group containing from 2 to 80 carbon atoms in which one or more carbon atoms are optionally replaced by a heteroatom selected from the group consisting xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, and xe2x80x94Nxe2x80x94 with the proviso that firstly no two oxygen atoms are joined together and secondly that at least one of A1 to A4 includes a polymerisable group;
B1 represents a hydrocarbon group containing from 4 to 80 carbon atoms, in which one or more carbon atoms are optionally replaced by a heteroatom selected from the group consisting xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, and xe2x80x94Nxe2x80x94 with the proviso that no two oxygen atoms are joined together;
MG1 and MG2 are the same or different and each independently represents an aromatic or non-aromatic carbocyclic or heterocyclic ring system containing from 2 to 80 carbon atoms, with the proviso that firstly at least one of MG1 and MG2 comprises at least two ring systems and secondly when MG1 and MG2 are identical either A1 and A2 or A3 and A4 are different or at least three of A1 to A4 are different.
The compounds of the invention are chiral or achiral and preferably have a substantially linear backbone, the groups A1, MG1, B1, MG2 and A2 being linearly arranged with respect to each other. It has been surprisingly found that the compounds of formula I can adopt a liquid crystalline mesophase over a broad thermal range. In addition they are characterised by melting points that are considerably lower than those of at least one of their mesogenic constituents. They are also valuable in the production of well-oriented LCP films having either a high or low optical birefringence and variable tilt.
For each of the groups A1 to A4, the term xe2x80x9chydrocarbonxe2x80x9d is understood to include straight-chain and branched alkyl, alkenyl and alkynyl groups as well as cyclic groups. The terms xe2x80x9calkylxe2x80x9d, xe2x80x9calkenylxe2x80x9d and xe2x80x9calkynylxe2x80x9d will accordingly be understood to include branched and straight chained groups. It will therefore be appreciated that one or more of the groups A1 to A4 may be selected from the group consisting of a C1-C20 alkyl, C1-C20 alkoxy, C1-C20 alkoxycarbonyl, C1-C20 alkylcarbonyl and a C1-C20 alkylcarbonyloxy group. Examples of C1-20 alkyl groups that may be present in the compounds of the present invention include, without limitation, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl and the like. Examples of C1-20 alkoxy groups that may be present in the compounds of the present invention include, without limitation, methoxy, ethoxy, n-propoxy, isopropoxy, butoxy, pentyloxy, exyloxy, heptyloxy, octyloxy, nonyloxy, decyloxy, undecyloxy, dodecyloxy and the like. Examples of C1-C20 alkoxycarbonyl groups that may be present in the compounds of the present invention include, without limitation, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentyloxycarbonyl, hexyloxycarbonyl, octyloxycarbonyl, nonyloxycarbonyl decyloxycarbonyl, undecyloxycarbonyl, dodecyloxycarbonyl and the like. Examples of C1-C20 alkylcarbonyl groups that may be present in the compounds of the present invention include, without limitation, acetyl, propionyl, butyryl, valeryl, hexanoyl, heptanoyl, octanoyl, nonanoyl, decanoyl, undecanoyl, dodecanoyl, terdecanoyl and the like. Examples of C1-C20alkylcarbonyloxy groups that may be present in the compounds of the present invention include, without limitation, acetoxy, propionyloxy, butyryloxy, valeryloxy, hexanoyloxy, heptanoyloxy, octanoyloxy, nonanoyloxy, decanoyloxy, undecanoyloxy, dodecanoyloxy, terdecanoyloxy and the like. Cyclic groups may contain up to 6 ring carbon atoms.
For the group B1, the term xe2x80x9chydrocarbonxe2x80x9d is understood to include straight-chain and branched alkylene, alkenylene and alkynylene groups. The terms xe2x80x9calkylenexe2x80x9d, xe2x80x9calkenylenexe2x80x9d and xe2x80x9calkynylenexe2x80x9d will be accordingly understood to include branched and straight chain groups.
Each of the hydrocarbon groups of A1 to A4 and B1 are optionally substituted by a substituent selected from the group consisting of C1-20 alkyl, C2-20 alkenyl, C2-20 alkynyl, C4-20 aryl, C3-20 cycloalkyl, C3-20 cycloalkenyl, C3-20 cycloalkynyl, amino, cyano, epoxy, halogen, hydroxy, nitro or oxo.
By the term xe2x80x9chalogenxe2x80x9d it should be understood to include fluorine, chlorine, bromine and iodine.
If a nitrogen containing group is used to replace one or more carbon atoms of the aforementioned hydrocarbon groups, this may be further substituted by a group selected from the group consisting of C1-20 alkyl, C2-20 alkenyl, C2-20 alkynyl, C4-20 aryl, C3-20 cycloalkyl, C3-20 cycloalkenyl and C3-20 cycloalkynyl.
The groups MG1 and MG2 are optionally substituted by a substituent selected from the group consisting of C1-20 alkyl, C2-20 alkenyl, C2-20 alkynyl, C4-20 aryl, C3-20 cycloalkyl, C3-20 cycloalkenyl and C3-20 cycloalkynyl, amino, cyano, epoxy, halogen, hydroxy, nitro and oxo.
In a first preferred embodiment of the first aspect of the invention, each or any of the groups A1 to A4 may be selected from a group of formula (II)
xe2x80x83Pxe2x80x94(Sp1)k1xe2x80x94(X1)t1xe2x80x94xe2x80x83xe2x80x83(II)
wherein
P is hydrogen or a polymerisable group selected from the group consisting CH2xe2x95x90CWxe2x80x94, CH2xe2x95x90Wxe2x80x94Oxe2x80x94, CH2xe2x95x90CWxe2x80x94COOxe2x80x94, CH2xe2x95x90C(Ph)xe2x80x94COOxe2x80x94, CH2xe2x95x90CHxe2x80x94COOxe2x80x94Phxe2x80x94, CH2xe2x95x90CWxe2x80x94COxe2x80x94NHxe2x80x94, CH2xe2x95x90C(Ph)xe2x80x94CONHxe2x80x94, CH2xe2x95x90C(COORxe2x80x2)xe2x80x94CH2xe2x80x94COOxe2x80x94, CH2xe2x95x90CHxe2x80x94Oxe2x80x94, CH2xe2x95x90CHxe2x80x94OOCxe2x80x94, (Ph)xe2x80x94CHxe2x95x90CHxe2x80x94, CH3xe2x80x94Cxe2x95x90Nxe2x80x94(CH2)m3xe2x80x94, HOxe2x80x94, HSxe2x80x94, HOxe2x80x94(CH2)m3xe2x80x94, HSxe2x80x94(CH2)m3xe2x80x94, HO(CH2)m3COOxe2x80x94, HS(CH2)m3COOxe2x80x94, HWNxe2x80x94, HOC(O)xe2x80x94, CH2xe2x95x90CHxe2x80x94Phxe2x80x94(O)m4 
xe2x80x83wherein
W is selected from the group consisting of H, F, Cl, Br, I and a C1-5 alkyl group;
m3 is an integer having a value of from 1 to 9;
m4 is an integer having a value of 0 or 1,
Rxe2x80x2 represents a C1-5 alkyl group; and
Rxe2x80x3 is selected from the group consisting of a C1-5 alkyl group, methoxy, cyano, F, Cl, Br and I;
Sp1 represents a C1-20 alkylene group, in which one or more methylene groups are optionally replaced by a heteroatom selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94Nxe2x80x94 or by linking groups such as xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CONxe2x80x94 or by an aromatic or non-aromatic carbocyclic or heterocyclic ring system containing from 4 to 10 carbon atoms with the proviso that no two heteroatoms are joined together,
k1 is an integer having a value of from 0 to 4;
X1 is selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94N(CH3)xe2x80x94, xe2x80x94CH(OH)xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94CH2(CO)xe2x80x94, xe2x80x94SOxe2x80x94, xe2x80x94CH2(SO)xe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94CH2(SO2)xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94OCOxe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Sxe2x80x94, xe2x80x94SOOxe2x80x94, xe2x80x94OSOxe2x80x94, xe2x80x94SOSxe2x80x94, xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94 and xe2x80x94Cxe2x89xa1Cxe2x80x94; and
t1 is an integer having a value of 0 or 1;
The term xe2x80x94Phxe2x80x94 in formula (II) is used to represent 1,2-phenylene, 1,3-phenylene and 1,4-phenylene respectively. The term (Ph) in formula (II) is used to represent phenyl.
The C1-20 alkylene group, Sp1 is optionally substituted by one or more substituents selected from the group consisting F, Cl, Br, I and CN. In addition one or more of the CH2 groups present in the hydrocarbon chain are optionally replaced by one or more groups selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94N(CH3)xe2x80x94, xe2x80x94CH(OH)xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94CH2(CO)xe2x80x94, xe2x80x94SOxe2x80x94, xe2x80x94CH2(SO)xe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94CH2(SO2)xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94OCOxe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Sxe2x80x94, xe2x80x94SOOxe2x80x94, xe2x80x94OSOxe2x80x94, xe2x80x94SOSxe2x80x94, xe2x80x94SF5, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94(CF2)xe2x80x94r, xe2x80x94(CD2)sxe2x80x94, xe2x80x94(CCl2)sxe2x80x94 and C(W1)xe2x95x90C(W2)xe2x80x94, in which W1 and W2 are each independently selected from the group consisting of H, H-(CH2)q1xe2x80x94 and Cl and with the proviso that no two heteroatoms are joined together. The integers r, s and q1 each independently represent a number of from 1 to 15.
It is preferred that the integers k1 and t1 each have a value of 1.
It is also preferred that X1 is selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94 and a single bond. It is especially preferred that X1 is selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94 and a single bond.
It is further preferred that Sp1 is a straight-chain C1-20 alkylene group. It is especially preferred that Sp1 is selected from the group consisting of ethylene. propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, and dodecylene.
It is still further preferred that P1 is selected from the group consisting of xe2x80x94CH2xe2x95x90CW5xe2x80x94 or CH2xe2x95x90CW5xe2x80x94(CO)v2Oxe2x80x94, in which W5 is selected from the group consisting of H, CH3, F, Cl, Br and I and v2 is 0 or 1.
In a second preferred embodiment of the first aspect of the invention there are provided compounds of formula (I) in which the group B1 is represented by the formula (III)
(X2)t2xe2x80x94Sp2xe2x80x94(X3)t3xe2x80x83xe2x80x83(III)
wherein
Sp2 represents a C4-20 alkylene group, in which one or more carbon atoms are optionally replaced by a heteroatom selected from the group consisting of xe2x80x94Oxe2x80x94 and xe2x80x94Nxe2x80x94 with the proviso that no two heteroatoms are joined together;
X2 and X3 are each independently selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94N(CH3)xe2x80x94, xe2x80x94CH(OH)xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94CH2(CO)xe2x80x94, xe2x80x94SOxe2x80x94, xe2x80x94CH2(SO)xe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94CH2(SO2)xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94OCOxe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Sxe2x80x94, xe2x80x94SOOxe2x80x94, xe2x80x94OSOxe2x80x94, xe2x80x94SOSxe2x80x94, xe2x80x94CH12xe2x80x94CH2xe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94 and a single bond; and
t2 and t3 each independently have a value of 0 or 1.
The compounds of the invention in which the group B1 is represented by the formula (III) have been found to be particularly easy to synthesise.
The groups X2 and X3 are preferably each independently selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94 and a single bond. It is especially preferred that the groups X2 and X3 are each independently selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94 and a single bond.
The group Sp2 is preferably a C4-20 straight-chain alkylene group. It is especially preferred that Sp2 is selected from the group consisting of propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene and dodecylene.
In a third most preferred embodiment of the first aspect of the invention B1 represents a group of formula (III) and at least one of A1 to A4 each independently represent a group of formula (II).
LCP materials prepared from the compounds of formula (I) have been found to be of particular use if they possess mesogenic properties. Such mesogenic properties may be achieved through the suitable choice of the groups MG1 and MG2. It is therefore preferred that at least one of the groups MG1 and MG2 has a mesogenic architecture.
It is preferred that at least one of the mesogenic groups MG1 and MG2 comprise at least two optionally-substituted aromatic or non-aromatic carbocyclic or heterocyclic ring systems. It is more preferred that one or both of MG1 and MG2 represents a mesogenic group comprising 1 to 4 aromatic or non-aromatic carbocyclic or heterocyclic ring systems having from 0 to 3 bridging groups, with the proviso that at least one of MG1 and MG2 includes at least two aromatic or non aromatic rings. MG1 and MG2 are optionally substituted by a group selected from the group consisting of C1-20 alkyl, C1-20 alkenyl, C1-20 alkynyl and a polar group such as xe2x80x94CF3, xe2x80x94SF5, xe2x80x94NO2, xe2x80x94CN, F, Cl, Br and I.
In a fourth preferred embodiment of the first aspect of the invention there are provided compounds in which the mesogenic groups MG1 and MG2 are represented by groups of formula (IV)
C1xe2x80x94(Z1xe2x80x94C2)a1xe2x80x94(Z2xe2x80x94C3)a2xe2x80x94(Z3xe2x80x94C4)a3xe2x80x83xe2x80x83(IV),
wherein
C1 to C4 each independently represent a non-aromatic, aromatic, carbocyclic or heterocyclic group containing from 2 to 10 carbon atoms.
Z1 to Z3 are each independently selected from the group consisting of xe2x80x94CH(OH)xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94CH2(CO)xe2x80x94, xe2x80x94SOxe2x80x94, xe2x80x94CH2(SO)xe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94CH2(SO2)xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94COCF2xe2x80x94, xe2x80x94CF2COxe2x80x94, xe2x80x94Sxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Sxe2x80x94, xe2x80x94SOOxe2x80x94, xe2x80x94OSOxe2x80x94, xe2x80x94SOSxe2x80x94, xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94OCHxe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94CHxe2x95x90CHxe2x80x94 and a single bond; and
a1, a2 and a3 are each independently 0 or an integer having a value of from 1 to 3. with the proviso that a1+a2+a3xe2x89xa63.
It is especially preferred that each of C1 to C4 are selected from the group consisting of 
wherein
L is selected from the group consisting xe2x80x94CnH2n+1, xe2x80x94C(O)CnH2n+1, xe2x80x94C(O)OCnH2n+1, xe2x80x94OC(O)CnH2n+1, xe2x80x94OCnH2n+1, xe2x80x94NO2, xe2x80x94CN, xe2x80x94SF5 and halogen;
n represents an integer having a value of from 1 to 20;
u1 represents 0 or an integer having a value of from 1 to 4;
u2 represents 0 or an integer having a value of from 1 to 3; and
u3 represents 0 or an integer having a value of from 1 to 2.
It is more especially preferred that C1 to C4 are each independently selected from the group consisting of optionally-substituted cyclohexyl, cyclohexylene, phenylene, phenyl, naphthyl, naphthylene, phenanthryl, phenanthrylene, decalinyl and decalinylene. Each of the groups C1 to C4 are optionally substituted by a group selected from the group consisting of C1-20 alkyl, C1-20 alkenyl, C1-20 alkynyl and a polar group such as xe2x80x94CF3, xe2x80x94SF5, xe2x80x94NO2, xe2x80x94CN, F, Cl, Br and I.
The compounds of the invention can be used to prepare devices containing a LCP material. It will be appreciated that the properties of a particular device will depend, in part, upon the nature of the compounds used to prepare the device. For example, materials having a high birefringence are generally required for the manufacture of retarder films or cholesteric filters having an elevated optical performance. LCP materials having a high birefringence can be readily prepared from compounds of formula (I) in which at least one of the groups MG1 and MG2 is highly birefringent. It has been found that a material with high birefringence can be prepared by using mesogenic groups that include at least two conjugated aromatic ring systems.
It is especially preferred that when materials having a high birefringence are required, each of the groups C1 to C4 are each independently selected from optionally-substituted phenyl, phenylene, naphthyl, naphthylene, phenanthryl and phenanthrylene; that a1, a2 and a3 are each independently 0 or an integer having a value of from 1 to 3; with the proviso that firstly 1 less than a1+a2+a3xe2x89xa63, and secondly that when each of C1 to C4 are phenylene, Z1 to Z3 are each independently selected from the group consisting of xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94CHxe2x95x90CHxe2x80x94 and a single bond. Each of the groups C1 to C4 are optionally substituted by a group selected from the group consisting of C1-20 alkyl, C1-20 alkenyl, C1-20 alkynyl and a polar group such as xe2x80x94CF3, xe2x80x94SF5, xe2x80x94NO2, xe2x80x94CN, F, Cl, Br and I.
Alternatively, there may be occasions where there is a requirement to use LCP materials having a low birefringence. It is, for example, preferred to use low birefringence LCP materials in the manufacture of optical polarisers characterised by short wave absorptions. Low birefringence LCP materials can be prepared from compounds of formula (I) having mesogenic groups MG1 and MG2 that contain no conjugated aromatic rings.
It is therefore especially preferred that, when materials having a low birefringence are required, the groups C1 and C4 are each independently selected from the group consisting of optionally-substituted phenyl, phenylene, cyclohexyl, cyclohexylene, decalinyl and decalinylene with the proviso that there are no directly connected phenyl or phenylene groups; that a1, a2 and a3 are each independently 0 or an integer having a value of from 1 to 3; with the proviso that firstly 1 less than a1+a2+a3xe2x89xa63 and secondly when C1 to C4 are each phenyl or phenylene, Z1 to Z3 are each independently selected from the group consisting of xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94OCH2xe2x80x94 and xe2x80x94CH2xe2x80x94. Each of the groups C1 to C4 are optionally substituted by a group selected from the group consisting of C1-20 alkyl, C1-20 alkenyl, C1-20 alkynyl and a polar group such as xe2x80x94CF3, xe2x80x94SF5, xe2x80x94NO2, xe2x80x94CN, F, Cl, Br and I.
The compounds of the invention may be readily prepared using methods that are well known to the person skilled in the art, such as those documented in Houben-Weyl, Methoden der Organischen Chemie, Thieme-Verlag, Stuttgart. The compounds may for example be made according to the reaction schemes 1-6 in which the following abbreviations are used:
DEAD is Diethyl azodicarboxylate
TPP is Triphenylphosphine
THF is Tetrahydrofuran
DMF is N, N-Dimethylformamide
Et3N is Triethylamine
BTSS is Bis(trimethylsilyl)sulfate
DBU is 1,8-Diazabicyclo[5.4.0]undec-7-ene
EDC is N-(3-Dimethylaminopropyl)-Nxe2x80x2-ethylcarbodiimide hydrochloride
DMAP is 4-Dimethylaminopyridine
(PPh3)2PdCl2 is Bis(triphenylphosphine)palladium dichloride 
Examples of compounds that may be synthesised according to the preparative methods of Schemes 1-6 are given below. This list is provided merely by way of example and should not be understood as limiting the scope of the present invention: 
The compounds of formula I can be used alone or as a component of a liquid crystal mixture. Liquid crystalline materials comprising a compound of formula (I) may be used in the manufacture of LCPs. A second aspect of the present invention therefore comprises a liquid crystalline material comprising a compound of formula (I). A liquid crystalline material according, to the second aspect of the invention preferably comprises at least two components. The additional components must be miscible with the compound of formula (I) and may be selected from known mesogenic materials such as those reported in Adv. Mater. 5. 107 (1993), Mol. Cryst. Liq. Crust. 307, 111 (1997), J. Mat. Chem. 5, 2047 (1995) or in patent applications U.S. Pat. No. 5,593,617; U.S. Pat No. 5,567,349; GB-A-2 297 556; GB-A-2 299 333; DE-A-195 04 224; EP-A-0 606 940; EP-A-0 643 121 and EP-A-0 606 939 and are preferably selected from EP-A-0 606 940; EP-A-0 643 121 and EP-A-0 606 939.
Liquid crystal materials comprising a compound of formula (1) may be used in the form of a single compound, a liquid crystalline mixture, a (co)polymer, an elastomer, a polymer gel or a polymer network. The actual form of the liquid crystal material will depend upon the application in which it is to be used. Polymer networks have been found to be of particular use and in a first preferred embodiment of the second aspect of the invention there is provided a polymer network comprising a compound of formula (I). The polymer network preferably comprises at least two components, at least one of which is a compound of formula (I).
The polymer network can be prepared by the copolymerisation of a mesogenic mixture comprising:
i) at least one mesogenic polymerisable compound;
ii) at least one compound of formula (I); and
iii) an initiator.
Polymer networks comprising a mesogenic polymerisable compound, a compound of formula (I) and an initiator may be used, for example, in the preparation of devices such as optical retarders. It will be appreciated that the components used in the preparation of the polymer network influence the properties of the network so prepared and that the choice of components will depend upon the application in which the polymer network is to be used. For example, in the preparation of devices such as cholesteric filters it is essential to include a chiral dopant as a component of the polymer network. A second embodiment of the second aspect of the invention therefore provides a polymer network comprising
i) at least one mesogenic polymerisable compound,
ii) at least one compound of formula (I);
iii) an initiator; and
iv) one or more chiral dopants.
The mesogenic polymerisable compound is chiral or achiral and may be a compound of formula (I). Alternatively or in addition, the polymerisable compound may be selected from the known mesogenic materials referred to above. Preferably the polymerisable compound has a thermotropic sequence which includes a nematic phase.
The polymerisable mesogenic compound may be present in an amount comprising 0.01 to 99% by weight of the liquid crystalline polymer network mixture, preferably 50 to 95% by weight.
The polymerisable LC mixture or LCP network preferably comprises a compound of formula (I) in an amount from 0.1 to 100% by weight of the liquid crystalline mixture or network, preferably from 1 to 50% by weight.
The initiator is preferably a photoinitiator and may be a radical or cationic initiator that is present in an amount comprising 0.1 to 5% by weight of the polymer mixture, preferably from 0.2 to 2% by weight.
The polymer network may comprise further components. These include additional polymerisable compounds, stabilisers and dyes. The additional polymerisable compounds are preferably non-mesogenic and include at least one polymerisable functional group. Diacrylate and vinylate compounds are especially preferred.
Stabilisers suitable for use in liquid crystal mixtures of the present invention are those having the ability to prevent undesired spontaneous polymerisation during, for example, storage of the mixture. Examples of suitable commercially available stabilisers include 4-ethoxyphenol and 2,6-di-tert-butyl-4-methylphenol (BHT). The second aspect of the invention therefore includes liquid crystalline mixtures including a stabiliser.
It may be necessary to add a dye to the liquid crystalline mixture if, for example. colour filters are required. It is, however, preferred to prepare liquid crystalline mixtures containing no dye.
When the mixture further comprises a stabiliser, this is generally present in an amount comprising 0.01 to 5% by weight of the liquid crystalline mixture, preferably from 0.1 to 1% by weight.
These polymerisable liquid crystalline mixtures and materials may be formed into liquid crystalline polymer (LCP) films and a third aspect of the invention provides a LCP film comprising a compound of formula (I). LCP films may be readily prepared by UV polymerisation of a LC mixture according to the invention; a film comprising the LC mixture is formed on a substrate and polymerised using UV light to give a cross-linked liquid crystal polymer (LCP) film. The film is both light and temperature stable and can be used in the manufacture of devices such as waveguides, optical gratings, filters, retarders, piezoelectric cells or thin films exhibiting non-linear optical properties.
Examples of substrates used in the preparation of LCP networks include transparent substrates such as coated ITO (indium tin oxide), glass or plastic. Preferred substrates include glass or plastic, especially those including a layer of rubbed polyimide or polyamide or a layer of photo-oriented photopolymer (LPP). The preferred substrates greatly facilitate uniform orientation of the liquid crystalline mixture.
In the preparation of LCP films, it is particularly important to prevent the formation of defects or inhomogenities. This can be achieved by forming the polymerisable liquid crystalline mixture into a thin film; the mixture is placed between two of the aforementioned substrates, which were then sheared over a small distance until a planar order was obtained. Alternatively the mixture can be capillary filled between two of the said substrates. In each case the mixtures are then cured using, for example, UV light, preferably in the presence of a photoinitiator. Suitable photoinitiators are commercially available and are well known to a person skilled in the art.
The liquid crystalline mixtures and films of the present invention can be used to prepare optical and electro-optical devices. A fourth aspect of the invention provides an optical or electro-optical component containing a liquid crystalline polymer film comprising a compound of formula (I). The optical or electro-optical component may be a waveguide, an optical grating, a filter, a retarder, a piezoelectric cell or a non-linear optical cell or film.
The invention will now be described with reference to the following non-limiting examples. Variations on these falling within the scope of the invention will be apparent to a person skilled in the art.
In the following Examples the thermotropic phases are abbreviated as follows:
K crystalline
D discotic
S smectic
N nematic
N* chiral nematic (cholesteric)
I isotropic